1. Field of the Invention
The present invention relates to a method and a system for cooling an internal combustion engine having charge air feed. The system includes a first and a second cooling loop, wherein the first cooling loop is operated at a higher temperature level than the second cooling circuit, and the charge air feed has at least one intercooling unit which is thermally coupled to the second cooling loop, in which a cooling throughput is controllable.
2. Description of the Related Art
Modern internal combustion engines, in particular diesel engines, typically have intercooling for cooling the air required for charging the internal combustion engine. Intercooling is required on one hand because of the heating up of the turbocharger due to the exhaust gases of the engine. The above-mentioned heating is caused by the joint arrangement of the turbine and the compressor on one shaft and consequently the thermal contact of the two housings. This thermal contact causes a heat transfer from the exhaust gas turbocharger to the charge air compressor.
On the other hand, one has to consider that the air taken in by the charge air compressor is typically heated to a temperature of approximately 180° C. or, with two-stage compression, to an even higher temperature. The charge air taken in expands with rising temperature, which causes a reduction of the oxygen proportion per volume unit. This reduction of the oxygen proportion causes a lower performance increase of the engine. To counteract this effect, the intercoolers mentioned above are used particularly in motor vehicle engines. The use of an intercooler ensures that the heated air is cooled down and thus a higher charge density is provided to the combustion process in the cylinder. Due to the higher oxygen content of the charge air per volume unit, it is thus possible to combust a larger fuel quantity. This results in a further performance increase which may be approximately 30%. Simultaneously, the nitrogen oxide emission is reduced by the intercooling because lower combustion temperatures are also achieved due to the lower charge air entry temperature.
In this context, a cooling system for internal combustion engines having indirect intercooling is known from U.S. Pat. No. 6,848,397. In the cooling system described, two air-cooled heat exchangers and an intercooler are provided in a cooling loop. The cooling system has an aggregate cooling loop for cooling an internal combustion engine, which comprises a main cooling loop having a main coolant cooler and an auxiliary cooling loop for cooling an auxiliary medium. The auxiliary cooling loop branches off at a decoupling point from the main cooling loop and leads back thereto at a coupling point, which is situated between the main coolant cooler and a coolant delivery pump. In addition to the two above-mentioned coolers, an intercooler is provided for cooling the charge air fed to the internal combustion engine. The technical achievement of the object described above has the essential feature that the cooling loops are operable at different temperature levels and the coolant delivery pump is adjustable in regard to the volume flow to be delivered, the delivery performance, and/or the delivery pressure.
As a supplement to the publication cited above, for example, a cooling system for supercharged motor vehicle engines is known from DE 10 2006 010 247, in which the intercooling unit has a charge air intermediate cooler and a charge air main cooler. Because in this case the charge air is compressed in two stages, the charge air is cooled between the low-pressure compressor and the high-pressure compressor using the intermediate intercooler, while the main intercooler cools the charge air which has left the high-pressure compressor.
The previously described systems have the disadvantage that, in each case the cooling loop operated at a lower temperature level and into which the intercoolers are also coupled, for example, is supplied with coolant in all operating states, so that the corresponding engine components are cooled at all times during operation of the internal combustion engine. However, independently of the minimum coolant throughput in the low temperature cooling loop, there are operating states of the internal combustion engine, such as the starting phase or specific phases for regenerating exhaust gas treatment components, in which an elevated temperature is needed.